Electrode construction for electrical precipitators



Dec. 5, 1950 w. M. SCHMIDT 2.5325

ELECTRODE CONSTRUCTION FOR ELECTRICAL PRECIPITATORS Filed March 22, 1948 s Sheefs-Sheet 1 I 25 25 as 68 INVENTOR.

ml. 752 MALCOLM 5CHMID7;

Dec. 5, 1950 w. M. SCHMIDT 2,532,734

ELECTRODE CONSTRUCTION FOR ELECTRICAL PRECIPITATORS Filed March 22,, 1948 3 Sheets-Sheet 2 4o a4 41 7 h 40 41 n f 41,; U 46 40 6 2 I 41 41 w g g!!! 53 E}:- IN V EN TOR.

I 2 MLTEEMALCOLM SCHMIDT, iiil in BY A7702 EYs.

Patented Dec. 5, 1950 ELECTRODE; CONSTRUGTION FORE, ELECTRICALtPRECIPITATORS-i Walter-MalcolmSchmidt, Lbs-Angeles; Califi", as-

signor to Western Precipitation; Corporation, LossAngelesgfialifasa corporation otzCaliforniwl Application March 22, 1948; Serial'vNi'). 16,244

. 1.; The present-invention relates-generally to-the electrical precipitation of suspended particles" from gases and" particularly directed to improved" collecting electrode structures" for such' electrical precipitatorsi Briefly, the -operation" of electrical precipitationi consists in passing gases; containing suspended fineparticles of either solid or liquid: through an 1 eleetriefleld. in- I whichthe particles become" electrically oharged= by attachment of" electrons or i'onsrand 'are then attractedto'anelee tri'cally charged. mem-ber'upon which-the charged particles area collected: It hasbeen common practice" to efiect charging of the suspended" particles by: passing then'r between l two opposed electrodes ibetween-:which a highpotential differ ence ismaintained; one of 'the two electrodes beinga discharge electrode zat iwhi'ch =there=issilent or: coronaelectrical discharge that ionizes the gas and' causes the-suspended particles 1 to-become charged; with the same-electrical-sig nas the dis charge; electrode This: is termed' chargingac 1310111- Ifr=thealsingle stage type nf precipitator, the= charged particles migrate under the influence of the electric field' between the electrodes-toward the other electrode which is a non-discharging electrodeof 'extendedsuriace, and collector-"become precipitated uporrathe 'surfaceof' 'thatelec trode, which is consequently termed the collecting electrode: In the two stage 0r 'separated field" type of preeipitator, the gas containing all or a substantial portion of tliecharged partic1es'passes into asecond or" precipitating field; typically-- maintained" between two opposed ncn discharg ing electrodes, and; under the-infiuence-of-the-= precipitating fleld; the-chargedparticles migrate to one of the elcctrodes between which the field is= maintained-and are deposited thereon: The-lat ter" electrode islikewisetermed a collecting elee- 1 The novel collecting electrode structure ofthepresentinvention is-hereinaftershown and trade.

described as i being" embodied in a precipitator 'ofthe single stage typebut' it will heunderstoow that the i'nventionis alsmapplicable to the two stage or "separated field type of preeipitaton The application of theinvention to the latter type"- of precipitator will be apparent to those'skilled in' the art from" the description.- below;

In the following description and'* in" the appended claims: the term "discharge" electrodes will be understood to designate an electrode which facilitates coronaldischarge:therefrom, because l. it" has aconfiguration: that establishes a sufli'ci'entlyhignpotential 'gradienvat ornear-its filiclaims. (01. 183? I surface to create corona discharge'before there is-a=disruptivedischargeor spark-over. For this purpose; the discharge electrode usually'takes the formof a member ofi smalllsurface area, such=as asmall diameterwireor a rod-provided'withsliarp edges or points; wherebytliere may-beecreated in the immediate" vicinity: of; the electrode asufli ciently' high. electric: field intensity to cause ionization and-:corona discharge; The term non discharging electrodeiwill lbe' understood to designate; an electrode that 1 minimizes: or prevents coronawdischargethereirom because it hasacon'w figuration that l establishes zaa-sufficiently low fields concentrationrat ori:near itsxsurfa'ce to tsuppressa the corona'discharge aatzelevatedipotentials.'lowen than the t.-voltage=required fortdisruptivedischargea or; spark-Fever. Florsthis purposea:nonedisohargsing; electrodexissusuallyg one of extended. surface; substantially freezfrom: sharp corners: or;v other: parts. of sharp surfacez curvature atuall portionss which are;v located. within the, electric; field so substantially to. avoid-ionization or= corona: dis-s charge. at thatelectrode. The; electrode of. the present. invention falls withimt'he category of: non-discharging. electrodes;

11: is a general object act the present invention to. devise; a collecting; electrode which; effects; a;

maximum. economy, in the construction of l a,- precipitator. This is. apartieularly important: tea.-

" ture, because of the. highinitiallcost of a prey cipitatorinstallation. In greater detail, itlisan objectoi-Jthe invention to devise a; constructionespecial importance: in the case of rebuilding a planter converting it to'an electrical precipitate? installation from some other type of apparatus for'dusfi collection: In? the latter case, it is-desirableto'utilize as much-of-the'existingstructureas possible; and therefore it isd'esirablethat'the parts" peculiar toan electrical precipitator be" readily adaptable'to'different designs.

It is als'oan important obj'ect of the invention to" providea collecting"electrode that is easy to rap and keep clean. Dust precipitated or col lected upon the collecting electrode usually adheres to the electrode to a greater or lesser extent and must be removed at frequent intervals in order to maintain the high efiiciency of the precipitator since the accumulation of dust upon the electrode changes the electrical properties of the system. Since the typical electrical precipitator installation is designed for continuous operation, or substantially so, it is necessary to clean the electrode effectively in a minimum length of time, perhaps either while the gas is still flowing or while the gas stream has been only momentarily diverted from the particular electrode being cleaned. Usually cleaning the electrodes is accomplished by striking them by means of a hammer; and it: is. desirable that the electrode structure be such that the shock of the rapper be transmitted throughout the entire electrode to jar loose the accumulated dust' deposit.

The above and other objects of this invention have been attained by providing a collecting electrode which comprises a suspended flexible sheetlike member. The support for the flexible member comprises in part a rigid hanger extending transversely across the top edge of the flexible member and resting upon fixed supporting elements. Guides or positioning means are provided for the electrode, which in a preferred form are vertically extending members located one at each vertical edge of the flexible member, to restrain the latter against undue horizontal movement. The flexible. member preferably comprises a plurality of generally spiral or. helicoform wire elements movably interconnected or loosely interwoven with other similar elements to leave relatively large openings between the wires, the plurality of wire elements forming a sheet-like member that is supported at its upper end and hangs in a substantially vertical plane within the side guides. The sheet-like member is especially flexible in a transverse plane since the several wire elements are loosely interwoven and movable with're'spect to each other.

Fixed support means for the hanger and guides are preferably located at the sides of the flexible member; and at each sidetypically comprises 5 a pair of spaced elements upon which a guide rests to be supported at-its upper end and which receive the guide by horizontal movement in one direction. The support means also support the hanger and the attached sheet-like member in a position such that the hanger confines the guide against horizontal movement in the reverse direction which would tend to unseat the guide from the fixed support means.

How the above objects and advantages of my invention, as well as others not specifically mentioned herein, are attained will be more readily understood by reference to the following description and the annexed drawings, in which:

Fig. l is a vertical cross section through a typical electrical precipitatorshowing the collecting electrodes of my invention installed therein, the

gas flowthrough thepre'cipitatorbeing in a di-.

rection parallel to the plane" of the'figure;

Fig. 2 is an enlarged elevation of a collecting.

electrode structure according. to'myinvention and supporting means therefor, together with certain adjacent parts of the housing structure;

Fig. 3 is a vertical section on line 3-3 of Fig.

2 through a typical oollectingelectrode, showing the supporting means in elevation,-certain of the parts being omittedto clarify the drawing;

Fig. 4 is a further enlarged fragmentary horizontal cross section on line fll of Fig. 2;

Fig. 5 is a further enlarged fragmentary front view of the support means for an electrode and the upper end of the electrode, viewed as in Fig. 3;

Fig. 6 is a further enlarged fragmentary elevation of a' portion of theup'per end of a collecting electrode and the supporting means therefor;

Fig. 7 is an enlarged vertical cross section through the upper end of several collecting electrodes, as on line 1l of Fig. 1, showing the attachment thereto or a rapper; and

Figs. 8 and 9 are, respectively, a fragmentary elevation and a vertical cross section of a variational form of linkarrangement for the flexible 'sheet. The precipitator is ordinarily enclosed within a housing or shell which is generally designated at H]. The shell is here shown as being made of metal, but it may be constructed of masonry or other suitable material. The shell is provided at one end with a gas inlet opening H and at the opposite end with a gas outlet opening [2 which communicate with any suitable type of ducts, not shown in the drawings, for conveying a dust-laden. streamof gas to and from the precipitator shell. Shell ii] is generally rectangular in cross section, except that the bottom is formed into a hopper l4 into which dust falls from the collecting electrodes. The dust is withdrawn from hopper l4 and shell it], either continuously or intermittently as may berequired, through bottom opening l5 which is connected to any suitable type or dust-conveying conduit, not shown. Shell Ill is ordinarily supported by connection to a building'or'a structural framework, the details of which constitute no part of the present invention and are therefore not illustrated herein; but as typical of such supporting framework, -the shell may be supported upon I- beams It. Through this supporting framework,j

prises a structural framework upon which a plu-V rality of discharge electrodes 26 is mounted. This frame in part resembles a cage and consists of vertically extending posts 2i to each of which are attached three horizontal members 22 which extend transversely of the direction of gas flow. The members 2| and 22 are ordinarily structural channels or angles, but maybe of any suitable shape. Horizontal members 22 support a plurality of other horizontal members, EfS andZSa. To a top horizontal member 23there is attached a pluralityof individualdischarge electrodes it so arranged that they are all in a common vertical plane. The lower horizontal members 23a guide or position-the discharge electrodes. Individual electrodes 2t maybe fine-wires of small diameter I or rods of polygonal cross section having rela- 1 tively sharpcorners at whicl -;.coro na discharge takesplace. a I

The frame carrying discharge electrodes 28 is suspended from hanger rods 25 connected to the upper endsof posts -ll and passing upwardly through the .top'wau of shell iii. Each hanger. rod 24..passesth1ough an insulatorv 25 which is located within housing .zeitnat is divided, into .xi-urip andlower sections. Each i'insulator fi isl enema :sunnorted @1 33 point intermediate:itsaendsqonxthe top wall of the .lower'zsectionsoi rxhousing :26.,:.1the .-.:,connection at ,this :point gbeing .gas .xtight. .Thus :.the interior :of the ;lower section of mousing- 26 -communicates with .theinterior :of shell 110 but not'with the uppersection of thepinsulatorhous- Line. "The .upperisectionof one 101 more :otin- :sulator shousings .226 ,is .made asgindicated :at 25c tin-Fig. 1 to receiveahigh.tension wire ZiBzwhich isaconnectedztoithe upperendxof arhangerirodgzd where it projects above insulator 25. By.me.ans of lead-in 28, electrical energy atahigh .voltage isapplied to the high tension discharge electrodes 1 from anysuitable source, not shown.

.Asmentioned above, electrodes :20 .shown .in Fig. 1 las suspended ;fr.om .horizontal ymember 23 ,arearrangedin a row in a common vertical plane -W1' i0h extends parallel to the direction of gas :flow. 'In order to handle alarge volume of .gas ;in.;a .precipitator, a plurality .of such .rows are -usually .arranged side-.by-side in parallel planes :spaced apart in a direction perpendicularto the :plane ofFig. 1. Thehorizontal members 23 and .23a for such other rows and the electrodes 20 sup- .aportedttherebyzaregsimilar in all respects to the :structure illustrated in Fig. l and are carried by-transverse members 22; and if the electrode supporting framework is large enough, additional ihangerrodsl l andinsulators are provided, ordinarilya totalof four being sufiicient unless the ,loadisveryheavy. The added insulator assemblies may conform to the construction shown at the left of Fig. ,1. The; arrangement of opposing electrodes inrows alternating between discharge and non-discharging electrodes with gas flow parallel to the extent of the rows is conventional practice in the art.

,As will be noticed by, reference to Fig. l, .the high tension electrodes arenarranged in groups, andopposing each of these groups of electrodes is collecting electrode, generally designated at 30, .ofthe non-discharging type; With the arrange- :ment shown in Fig. 1, there are three such colvlecting electrodes .32 disposed in one row in a common vertical plane parallel to the vertical plane of arow of discharge electrodes 20. The details ofconstruction .of these collecting electrodes are shown more particularly in .Figs. 2 et seq.

.As may be seen in Fig. 2, each complete collecting electrode structure comprises a flexible sheet-like member 62 which is the electrode properand'is supported atits upper end byitrans- .yersely extending hanger .33 that is fastened to sheet .32 by anysuitable means, as bolts 34. The flexible sheet-like memberr32 is like awire mesh screen, being composed of a plurality of helicoform wire elements which'are flexiblyor movably interconnected, as :by being loosely interwoven with eaclrother. '.The openingsbetween the wires are relatively large compared with the wire, as may beseen in-Fig'G. .It is quitesatisfactory that the least dimension .of each opening between the wires be several times the diameter of the wires themselves. .For example a -wireof. approximately .1" diameter and an opening of about are satisfactory dimensions .under most conditions. A smaller :opening unnecessarily increases the weight of the electrode without'increasing its efficiency; :andthererisa decrease in'the efficiency of the electrode if thesize of the opening is tooreat.

'iT-he several wire elements of the-electrode sheet are: described "as .helicoform since, although they mayaibetrue circular :spira1s,.:1t is preferablexthat .zthey tiactually rbe :a somewhat r rflattened zepiral :when :yiewedaendwise, as may -=be-:seen inrEigiS, was athis :change :in shape :fromea a'true ccirele "has ,the aefiectcofmeducingrthe .thicknessaof rthe :sheet and increasing itsaventical dimension, and consegquentlyithezareazof thegsheet,-foriargiven weight. The taxes .of these helicoform wire. elements are parallel to each other and are horizontal onsub- ;stantially..so. ;In the (form rof ;screen .shown in Riga-Brand ;6, :the'iwire :elementsrare :eachloosely .:interw oven .with a similar e1ement .:above .and ibelnw it. ilhere :being no .rigid wconnectionwbe- --.tween two .l-interlocking 1 spirals, ythe spirals are .ifreeito swing with respect \to each other :in .a transverse plane; :and consequently the :sheet .is :extremely flexible in. a;-transverse yertical ,plane, :which 11S ;;a plane perpendicular to :the 1 plane :of Fig. {2 :when the. sheetds suspended. .At .the .same itime, :the sheet as a wholewhasrrelatively little :flexibility .--in a transverse; horizontal ;plane per- ;pendicular Lto the plane=of Fig. ,2 :and. even ;less flexibility in-thezplane of :the drawing, This-nex- ..i-bility1 ojf the sheet-like member taken as a whole, monies-about largely because of. the nature .of the interconnections between .the helical elements composing thesheegbecause the fiexibilitylor resiliency .of each individual element is roughly rthe same in anyldirection,although it may diifer somewhat ;in variousdirections depending upon :theamount :of flattening of lthespiral.

Hanger {33 .from .whiohesheet 32 is "suspended imaytake any convenient form, butdszhereshown as-being .cornposedlof a-; pair .of anglesplacedback .to back with .sheet 32 clamped between the two :parallel legs of the ,angles. Hanger .33 extends to the vertical edges of sheet 32 at-leach end.

;;Sheet ;'3 2 visnonfined atzeaich of. itsqvertical-edges :by guide ror positioning :means that engages. the :sheet below the :to hanger, and preferably .is :channel-shaped guide membere35, shown in cross section in Fig.4. .Sheet 532 .-is;not attached to .channel 351nor is it clamped therein, but there is .suflicient iclearance all around .the sheet to enable the .sheet toslide or vibrate freely within .theechannel. cHowever guides 1.3 5 impart -adesirable .degree :of :rigidity to Lthe .-,.ele,c.trode structure and prevent :sheet 32 .trom swinging freely toward and away from electrodes 20. Eleetrode sheet 32 normally hangs istraightand vertically under its .:own weight, :but it is desirable that guidesibe 'providedzimorder to;;constrain the elec- -ztrodez-ragainstztundue horizontalrmovement, since any substantial .ehange {in the ;:spacing between electrode 2.32 and :elecllrodes 2|! .is to 'be avoided. lnhorder' to add to "the rigidity of the electrode structure iasaaywhole; thertwoiside channel guides 3.5 may: bezloosely connected atztheirrlower ends bymrossbarsflfi.

"In .order to :improve gas rdistribution rand allow through the .zprecipitator, .each .guide .35 is "providedawith bellies :31 :which are flatwertically extendingrplatesattachedtothe .outenfaceo'f channelsl35. {The t,use.of such zgas baffles is entirely optional'rbuta;='serves to: shield the-surface of cob lecting electrode 32 torsome extent; from the gas stream. ass-explained aboveandishownin :3, theprecipitatoriconsistsl-of .a.:series-:.of alternating discharge electrodeassemblies and -.collecting electrodezstructures"arrangedsideeby:side in verticaliaplanes, asishownzi-n Fig.1; andgas flow between zeach'stwoseollecting electrodes, is equalized to some extent by baffles .31, .since they prevent the rhulk 0f tthegasstream from flowing through the central a ortion cof the '1 recipitator, "where resistanceatolflowsis'zataaaminimum. ffiherhaflleat each side of the channel is made in two sections attached in the positions shown rather than as a single continuous baflle throughout the entire length of the channel in order to provide the necessary electrical clearance between the collecting electrode structure and the supporting framework for the discharge electrodes which is at high potential.

The fixed supporting means for the complete collecting electrode structure includes a horizontally extending angle member 40 upon the outer vertical face of which is mounted a pair of brackets 4|. The two angle brackets 4| extend horizontally out from the face of the member 40 and are arranged facing each other, but spaced apart, as may be seen best in Figs. 3 and 5. A plurality of pairs of such brackets 4| are arranged at regular intervals along angle 40 to support successive electrode structures 30, as may be seen from'Fig. 3. Considering for a moment only the lower legs 4|a of brackets 4|, it will be seen that these legs present a pair of downwardly converging and upwardly disposed faces. A guide 35 is prepared to be supported upon these faces by flaring outwardly the upward ends of the sides of the channel, in the manner shown in Fig. 5, so that the flared sides of the channel guide rest upon the upwardly disposed faces of elements =4|a. In preparing the upper end of guide 35, the back of the channel is cut awa at 35a above the bend in the sides, and plate 42, approximately square in shape, is welded to the channel guide along the line 35a, and also to the flared sides of the channel. In this way plate 42 braces the flared sides of guide 35 to hold them apart in the proper position.

Each guide 35 is hung upon brackets 4| by moving the upper end of the guide horizontally into the space between the two brackets and allowing the guide to drop downwardly until its flared sides come to rest upon the downwardly converging upper faces ofbracket elements 4| a. Brackets 4|, without any guide in them are shown at the extreme right in Fig. 3, while the brackets with'a' guide only supported on them are shown at the center of Fig. 3. This spacing between brackets 4| is such as to take guide'35 with slight clearance. I j

The upper legs 4|b of anglebrackets 4| act as holddown members to'engage plate 42 and prevent channelguide 35 from being displaced up:- wardly from the supporting means. Elem'ents -4 lb also engage directly hanger 33. Thus hanger 33 rests" upon the top of brackets 4| allowing the mesh sheet 32 to pass downwardly between brackets 4| and into the channel guide at each vertical edge of the sheet. Although each leg4|a and Mb can be made as a physically separate member if desired, it is preferred for obvious reasons to make them inpairs as a single bracket 4|.

As shown in Fig.2, the supporting means for the vertical guide and hanger '33 is similar at each side of electrode structure 30. The "horizontal length of hanger 33 is such thatit'slide'sdown easily with'a'mpl'e clearance between the two angles 45 at either side of electrode 3 but hanger 33 is-long enough that it cannot be displaced from a supporting bracket 4| merely by longitudinal movement. As may be seen in Fig. '6 the upper'endof each vertical guide 35 asrepresented byplate 42'ls between the end of hanger 33 and the outer vertical face of angle 40. In this way the guideis held securely against horizontal movement which would displace it from support ing brackets 4|, i. e., horizontal movementinthe directed blow.

8 reverse direction to that which is used to seat the guide on the supporting brackets.

Each angle 40 is supported upon a bottom flange on an inverted channel which extends transversely across the upper portion of the precipitator housing l0 and forms a part thereof, as shown in Fig. l. Angles 40 are removably held in place by bolts 46 which carry spacers 4! that maintain the proper distance between the vertically extending portions of angle 40 and channel 45.

At the bottom of shell [0, are horizontally ex tending braces 5|] which are located directly beneath channels 45, as may be seen in Fig. 1. Each brace 50 comprises a pair of horizontally extending channels 5| interconnected by lattice bars 52. Lattice bars 52 are preferred to plates in order that precipitated dust does not pile up on-to'p of the braces. Braces 53 carry on their side faces channels 53, and are spaced apart horizontally the proper distance to receive between channels 53 the lower ends of electrodes 30, as shown in Fig. 2. Horizontally extending pins 54 are mounted on channels 53 in pairs, as shown in Fig. 3. The lower end of each guide fits between a pair of pins 54 and is positioned thereby to keep the guides parallel to each other and to the discharge electrodes. Guides 35 cannot move toward each other at their lower ends because ofbar 33; and so pins 54 and channels 53 provide posi; tioning means for holding the lower ends of the guides against horizontal movement but still permit the guides to move vertically.

There is shown in detail in Fig. 7 a typical construction whereby the collecting electrodes may be rapped and the accumulated dust jarred loose. A pair of channels 53 are placed back-to-back and extend transversely across the top of a number of electrodes 3|). The channels 58 rest upon hangers 33 and are firmly bolted thereto by bolts 53. A vertical rod 50 is bolted to channels 58 at 5! and passes upwardly through shell 55. A gastight fit where rod 65' leaves the shell is obtained by placing packing 54 between rod 60 and sleeve surrounding rod 6| Rapper 63 is mounted upon the upper end of rod 65, and may be any one of a number of suitable types of rappers. The rapper 68 herein shown is of the pneumatic type and comprises an internal hammer (not shown) which is intermittently driven against an anvil by air pressure to create a shock which is transmitted by rod 60 and channels 58 to hangers 33 and flexible sheets 32. The shock is sufliciently violent that the vibration set up in the electrodes jars'loose the accumulated dust on the collecting electrodes and the dust falls down into hopper i4.

In the particular arrangement shown in Fig. 7, the hammer in rapper 68 strikes an upwardly As a consequence the shock wave transmitted to the flexible sheets 32 travelsvertically or in a direction transversely to the'general extent of the individual wire elements in each electrode 32. Thiscauses each of the wire elements to be moved" relative to adjacent ele.- ments, and this relative movement of the elements is very effective in breaking loose the dust accumulations. Since the flexible member 32 is not attached to guides 35 or cross bar 33, the minimum amount of weight is lifted and vibrated by the rapping mechanism, and the flexible sheet is free to move independently of the constraihe ing guides around its border. At the same time, by virtue of the manner inwhich the guides and hanger .are locked in the supporting brackets .4l,

9; guides 35 are securely" held against any movementtwli-ic'hwouldz displace. them fromtheir support during rapping.

It will be apparent from the-foregoing description of the present invention, that the construction readily lends itself to a maximum of shop labor and aminimum of-fleld labor forerection. The-wire mesh-sheets-M-can'be out to size in the shop and the hangers 33-boltedatone end. Each electrode can then be shipped by using the hanger as a core upon which to roll the flexible sheet of the electrode, thus making a package which is easily handled and crated and which is not subject to being easily damaged in shipment, as is the case with plates or other rigid members which have a surface area comparable to that afforded by the wire mesh curtain when it is in place in the precipitator.

The side guides 35 can be completely shop fabricated, and need no bolting or welding to hang them in place, except for attaching the cross bar 36 to each pair of channel guides.

Erection of the electrodes is particularly simple since, after hanging the two channels in place on brackets 4|, the lower end of sheet 32 is inserted in the guides, and the electrode slides downwardly between the guides into place. This can be done as the electrode is unrolled from around hanger 33, assuming that it has been rolled for shipment as described above. As the flexible sheet slides downwardly in the side guides, hanger 3%! drops into place, completing, the structure and by its own weight securing itself in place.

The addition of the rapping mechanism is easy since the cross channels 58 are merely laid upon the tops of hangers 33 and bolted thereto.

It will also be evident from the foregoing description that this electrode construction is very easily adapted to precipitator housings of various sizes and shapes and can be used equally well with precipitators which are completely designed and built as a unit or those in which existing structures are used for the shell and only the electrodes are installed.

Although there is shown in Figs. 5 and 6 a form of woven wire mesh in which the helicoform elements are interwoven with each other it will be apparent that the same physical characteristics and advantageous results are obtained if the sheet 32 is made of the same helicoform elements which are loosely interconnected with each other by means which permit them to move freely with respect to one another. A sheet 32a of this type is illustrated in Figs. 8 and 9 in which the helicoform elements 15 are interconnected by means of transversely extending rods H. Since there is no weld or cement or other material forming a rigid joint at the connection of two of these elements, it will be seen that the modified form of wire mesh illustrated in Figs. 8 and 9 may be used in place of that described earlier.

Having described a preferred embodiment of the present invention, it will be readily appreciated that various changes in the construction and detailed arrangement of parts may be made by persons skilled in the art without departing from the spirit and scope of my invention; and con sequently it is to be understood that the foregoing description is considered as being illustrative of, rather than limited upon, the appended claims.

I claim:

1. A collecting electrode structure for an electrical precipitator comprising: a flexible sheetlike member; a rigid hanger attached across the topl edge of the flexible member and adapted to suspend the flexible member; a. vertically extendingguide at'eachvertical'edge ofthe flexible member loosely restrainingthe flexible member.

against horizontal movement but permitting rela-- tive verticalmovement; and supporting means for supporting the guides independently of the hanger.

2.. A. collecting electrode structure for an. electrical, precipitator comprising a flexible sheetlike member; a rigidh-anger attached across the top edge of the flexible member; a U-shaped vertically extending guide at each vertical edge of the flexible member loosely restraining the flexible member against horizontal movement; and a fixed support means for the hanger and guide located at each side of the flexible member, the guide and hanger being independently supported in said support means.

3. A collecting electrode structure for an electrical precipitator comprising a flexible sheetlike member; a rigid hanger attached across the top edge of the flexible member; a U-shaped vertically extending guide at each vertical edge of the flexible member loosely restraining the flexible member against horizontal movement; and a fixed support means for the hanger and guide located at each side of the flexible member, comprising supporting elements adapted to receive the upper end of the guide by horizontal movement in one direction and to support the hanger in a position to confine said upper end of the guide against horizontal movement in a reverse direction,

4. A collecting electrode structure for an electrical precipitator comprising a flexible sheetlike member; a rigid hanger attached across the top edge of the flexible member; a U-shapcd vertically extending guide at each vertical edge of the flexible sheet loosely restraining the flexible member against horizontal movement, the sides of the guide being flared outwardly at the top end; and fixed support means for the hanger and guide located at each side of the flexible member, comprising a pair of spaced elements 1 having upwardly disposed and downwardly converging faces on which the flared sides of the guide rest, and second pair of spaced elements above the first pair for supporting the hanger with the flexible member passing downwardly between both said pairs of elements.

5. A collecting electrode structure for an electrical precipitator comprising a flexible sheetlike member; a rigid hanger attached across the to edge of the flexible member; a U-shaped vertically extending guide at each vertical edge of the flexible sheet loosely restraining the flexible member against horizontal movement, the sides of the guide being flared outwardly at the top end; and a fixed support means for the hanger and guide located at each side of the flexible member; comprising a pair of spaced facing angle brackets the lower legs of which provide downwardly converging faces on which the flared sides of the guide rest, and the upper legs of which brackets support the hanger in a position to hold the guide in place on the brackets.

6'. A collecting electrode structure for an electrical precipitator comprising a flexible sheetlike member; a rigid hanger attached across the top edge of the flexible member; a U-shaped vertically extending guide at each vertical edge of the flexible sheet loosely restraining the flexible member against horizontal movement; fixed support means for the hanger and guide located at each side of the flexible member, comprising sup- 11=- porting elements adapted to receive the upper REFERENCES CITED end of the gulde by horizontal movement m one The following references are of record in the direction and to support the hanger in a position to confine said upper end of the glide against p this patent horizontal movement in a reverse direction; and 5 FOREIGN PATENTS positioning means engaging each guide near the N mb Country Date lower end to position the guide at its lower en 337,490 Germany June 9, 1921 and hold it against horizontal movement while 459,808 Germany May 16, 1928 permitting vertical movement relative theret 747,904 France Apr. 4, 1933 WALTER MALCOLM SCHMIDT. 1o 

